6 Answers
6

You probably did a copy that preserved the original group and owner of these files. Within linux internally the owner and group is basically just an id (in your case, the number 515). This id is then mapped on a group and user name listed in /etc/passwd or /etc/group. You will see that in those files, you can find the name of the user and also the id used for that specific user and group.

Most likely in the /etc/group and /etc/passwd, the id "515" is not listed, and for this reason the id itself is shown.

You can change the ower and group to an existing owner and group with the commands chown and chgrp respectively.

The numbers can be three digits or four digits. Four digits have a more special purpose and if you are curious, read the chmod documentation.

The first digit is the user, the second digit is the group, and the third digit is all others. That is going from left to right, in case there are any confusions there. So in actuality, when you do an ls -l you'll see nine spaces (read, write, and execute for user, then group, then others).

For octal notation, remember these three numbers and their purpose:

4 Read
2 Write
1 Execute (search in directory)

like if yoiu want to set the read execute and write permission for the user, write and read for the group and read for user then the notation would be

**u** **G** **o**
4+2+1 4+2 4
7 6 4

i hope it will clear the concept

in your case 5 1 5 means read and execute permission to the user, execute to the group and read and execute to others.

You have completely missed the point of the question. The op is not asking about file permissions (which is what you are addresssing)... rather, the question is about the identifiers assigned to users and groups.
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TheGeeko61Jan 16 '12 at 2:09